1. Field of the Invention
The present invention relates a graphene wafer, a method for manufacturing a graphene wafer, a method for releasing a graphene layer from a substrate, and a method for manufacturing a graphene device.
2. Description of the Related Art
The Scotch tape method as a transfer technique of graphene was reported in 2004 by A. Gaim et al. of Manchester University in United Kingdom. They succeeded in mechanically transferring a single layer of graphene onto an SiO2/Si substrate from a highly oriented pyrolytic graphite (HOPG).
Graphene is a massless Dirac fermion material having a unique band structure and provides almost all useful electrical properties of carbon nanotubes having a structure of a tube including ballistic conduction, which will attracts engineer interest. Graphene is a new material having a sheet-like structure as opposed to carbon nanotubes (CNT), and therefore lends itself to micromachining used in conventional LSI technology, facilitating the integration of circuits.
After the discovery of graphene, releasing a sheet of graphene from an HOPG is apparently the only way of obtaining a high quality graphene sheet. Thus, a graphene sheet having a large area is difficult to obtain, which is an obstacle to the process for manufacturing integrated devices.
Japanese Patent Application Laid-Open No. 2009-62247 discloses a technique in which an SiC substrate is subjected to high temperature hydrogen etching and high temperature heat treatment in vacuum so as to manufacture and transfer a sheet-like epitaxial graphene (i.e., graphene sheet) layer on the SiC substrate.
An epitaxial graphene layer formed on an SiC substrate has a crystal surface which is flat at the atomic level and is chemically firmly bound, so that chemical adhesion techniques which use a variety of conventional adhesives fail to release the epitaxial graphene layer in its entirety from the entire surface of the SiC substrate. Consequently, this epitaxial graphene layer is difficult to transfer in its entirety onto another substrate.